Oxidation resisting hydrocarbon products



Patented Nov. 18, 1952 OXIDATION RESISTING HYDROCARBON PRODUCTS John G. McNab, Cranford, Niilo V. Hakala, Rahway, and John P. McDermott, Springfield, N. J assignors to Standard Oil Development Company, a corporation of Delaware N Drawing. Application February 27, 1951, Serial No. 213,054

2 Claims. 1 Y

The present invention relates to the improvement of hydrocarbon products and in particular to the improvement of mineral lubricating oil compositions by the incorporation therein of an additive which imparts oxidation resisting properties to such products.

This'is a continuation-in-part of application Serial Number 788,670, filed November 28, 1947, now Patent No. 2,552,570, patented May 15, 1951.

In the development of petroleum lubricating oils the trend has been to use more and more efficient refining methods in order to reduce the tendency of the oils to form carbon and deposits of solid matter or sludge. While such highly refined'oils possess many advantages, their resistance to oxidation particularly under conditions of severe service is generally decreased and they are more prone to form soluble acidic oxidation products which are corrosive. They are generally less efiective than the untreated oils in protecting the metal surfaces which they contact against rusting and corrosion due to oxygen and moisture. They also often deposit thick films of varnish" on hot metal surfaces, such as the pistons of internal combustion engines.

In accordance with the present invention it has been discovered that the tendency of refined mineral lubricating oils and other hydrocarbon products to corrode metal surfaces, particularly the surfaces of copper-lead and cadmium-silver bearings which are employed in internal combustion engines, is markedly reduced by adding a small proportion of cuprous di-(methylcyclohexyl) dithiophosphate. It is well known that many compounds of copper, especially certain organic salts such as copper naphthenate, as well as metallic copper, tend to promote the oxidation of organic material such as hydrocarbons. Most, if not all, of the copper compounds having this property are cupric, that is, higher valent compounds. It has been found, moreover, that the corresponding cupric di-(methylcyclohexyl) dithiophosphate is definitely inferior to the cuprous compound in corrosion inhibiting properties and at the same time it markedly increases th tendency of the base oil to deposit varnish on engine parts.

The compound which is employed as an antioxidant additive in accordance with the present invention is believed to have the formula where represents a methylcyclohexyl radical.

This compound may be readily formed by heating methylcyclohexanol with phosphorus pentasulfide in the proportions of 4 mols of the former'to l of the latter, and neutralizing the di-(methylcyclohexyl) dithiophosphoric acid thus formed with cuprous oxide, using 2 mols of the acid to 1 mol of the oxide. The neutralization reaction may be carried out in a light mineral oil medium and takes place on contact of the reactants. The salt concentrate thus formed may then be conveniently employed in blending with a lubricating oil base.

For general antioxidant purposes and particularly when the additive is to be employed in a lubricating oil, the amount of the additive will range from about 0.02% to about 3%, and the particular amount in individual cases will be selected in accordance with the requirements of the case and in view of the properties of the base stock employed.

The preparation and testing of samples of the additive of the present invention as well as samples of the corresponding cupric salt for comparison are illustrated by the examples to be described in detail below, but such examples are not to be construed as limiting the scope of the invention in any manner.

EXAMPLE 1 Cuprous di-(methylcyclohemyl) dithiophosphate (preparation A) A B-necked, l-liter flask equipped with a stirrer, reflux condenser and thermometer, was charged qwith 228 g. (2 mols) of methylcyclohexanol and 111 g. mol) of PzSs. This mixture was heated .with stirring at 110 C., for 30 minutes, after which the resulting dithiophosphoric acid was poured into a 3-liter beaker containing 514 g. of a light lubricating oil of approximately SAE was found to contain 7.3% copper, 7.1% sulfur,

and 3.4% phosphorus. I

EXAMPLE 2 Cuprous di-(methylcg clohexyl) dithiophosphate (preparation B) n A further preparation of cuprous di-(methyl :cyclohexyl) dithiophosphate was carried outin a manner similiar to that described in Example 1. This product (35% concentrate) was found to contain upon analysis 5.72% copper, 5.89% sulfur, and 2.99% phosphorus. The neutralization number was found-to be 4.74.

EXAMPLE 3 Preparation of cupric di-(methylcyclohearyl) dithiophosphate This composition was prepared in a manner similar to that described in Examples 1 and 2, except that twice the amounts of the methylcyclohexanol, phosphorus pentasulfide, and mineral oil medium were used with 80 g. (1 mol) of cupric oxide. The product (35% concentrate) upon analysis was found to contain 2.99% copper, 6.44% sulphur and 2.77% phosphorus. The neutralization number was found to be 15.4.

EXAMPLE 4 Laboratory bearing corrosion test A blend containing 0.25% of the active ingredient of the cuprous di- (methylcyclohexyl) dithiophosphate, prepared as in Example 1, in an extracted Mid-Continent parafiinic lubricating oil of SAE 20 grade and a sample of unblended base oil were submitted to a laboratory test designed to measure the effectiveness of the additive in inhibiting the corrosiveness of a typical mineral lubricating oil towards the surfaces of copperlead bearings. The test was conducted as follows: 500 cc. of the oil was placed in a glass oxidation tube (13 inches long and 2% inches in diameter) fitted at the bottom with a inch air inlet tube perforated to facilitate air distribution. The oxidation tube was then immersed in a heating bath so that the oil temperature was maintained at 325 F. during the test. Two quarter sections of automotive bearings of copper lead alloy of known weight having a total area of 25 sq. cm. were attached to opposite sides of a stainless steel rod which was then immersed in the test oil and rotated at 600 R. P. M., thus providing sufficient agitation of the sample during the test. Air was then blown through the oil at the rate of 2 cu. ft. per hour. At the end of each 4-hour period the bearings were removed, washed with naphtha and weighed to determine the amount of loss by corrosion. The bearings were then repolished (to increase the severity of the test), reweighed, and then subjected to the test for additional 4-hour periods in like manner. The results are given in the following table as corrosion life, which indicates the number of hours required for the bearings to lose 100 mg. in weight, determined by interpolation of the data obtained in the various periods.

Bearing Oil Sample Corrosion Life (Hrs.)

Base oil 9 Base oil 0.25% Cuprous di-(methylcyclohexyl) dithiophospliate (Ex. 1) 27 EXAMPLE Lauson engine test at 300 F. jacket temperature, 295 F. 011 temperature, 1800 R. P. M. speed and 1.5 indicated kilowatt load, the tests being conducted for 25 hours each. The loss in weight of the copperlead bearings and the varnish demerit were determined in each test. The varnish demerit rating was based upon a rating scale in which a perfectly clean piston surface is given a rating of 0 and a demerit of 10 is given to the worst condition which could be expected to exist on that EXAMPLE 6 Copper strip corrosion test Copper strip corrosion tests were made on blends of 1.5% each (0.52% active ingredient) of the oil concentrate products of Examples 2 and 3, and on'a sample of the unblended base oil, which was the same as that employed in Example 5. The test was a modification of the C. R. C. method 11-16-445 for determining copper staining tendencies of oils, the method as modified comprising immersing a polished metallic copper strip in the oil to be tested fora period of 3 hours at 210 F. and noting the extent of staining. Ratings are given on a scale of from 1 to 10 which denotes discoloration ranging from no stain to a black surface film. The test'results are as follows:

1 Copper Oil Sample i Base oil 3 Base oil 0.52% Cuprous di-(methylcyclohcxyl) d oohosphate (Ex. 2)

Base oil 0.52% Cupric di-(mcthylcyclohcxyl) dithi- I opliosphate (Ex. 3) 8 EXAMPLE 7 Robinson color test The Tag Robinson color test was applied to 1.0% and 2.0% concentrations of each of the oil concentrate products of Examples ,2 and 3 in the same base oil as that employed in Ex:- ample 5 and to a sample of the unblended base oil. The results are as follows:

EXAMPLE 8 Aluminum cup coking test This test is designed to measure the stability or coking tendency of aviation oils at very high temperatures, a factor of extreme importance in the opera-tionoi aviation engines of the Pratt and Whitney R4360 type. The test 011 is charged to a weighed aluminum cup which is heated with an electrical jacket and fitted with a stirrer placed from the cup bottom. The stirrer is started and the oil temperature is raised to 550 F., when the stirrer is stopped for 10 minutes. The stirrer is then operated for 10 minutes and stopped again for 10 minutes for a total of four 10-minute ofi cycles. During the test the oil temperature is kept at 550 F. and the jacket temperature at 500520 F. At the end of the test the oil is poured from the cup which is then washed with naphtha and dried with air to a constant weight. The difference in the weight of the cup before and after the test is taken is the amount of coke deposit. This test was applied to a solvent extracted Mid- Continent aviation type lubricating oil of 100 seconds viscosity (Saybolt) at 210 F., to which had been added, in separate samples, 2.5% of each of the cuprous and cupric di-(methylcyclohexyl) dithiophosphate concentrates (0.87% active ingredient) prepared as in Examples 2 and 3. A sample of the unblended base oil was similarly tested. 75 g. of sample was used in each test. The results were as follows:

It can be seen from the above data that cuprous di-(methylcyclohexyl) dithiophosphate is a valuable additive for mineral lubricating oils in a number of respects and that it is definitely superior to the corresponding cupric compound. The cuprous compound inhibits corrosion to a marked degree without increasing the deposition of varnish, and it inhibits the tendency of the base oil to form coke at high temperatures.

The additive of the present invention may be employed not only in ordinary hydrocarbon lubricating oils but also in the heavy duty type of lubricating oils which have been compounded with such detergent type additives as metal soaps, metal petroleum sulfonates, metal phe- A nates, metal alcoholates, metal alkyl phenol sulfides, metal organo phosphates, phosphites, thiophosphates, and thiophosphites, metal xanthates and thioxanthates, metal thiocarbamates, and the like. Other types of additives, such as phenols and phenol sulfides, may also be present.

The lubricating oil base stock used in the compositions of this invention may be straight mineral lubricating oils or distillates derived from parafiinic, naphthenic, asphaltic or mixed base crudes, or, if desired, various blended oils may be employed as well as residuals, particularly those from which asphaltic constituents have been carefully removed. The oils may be refined by conventional methods using acid, alkali and/or other agents such as aluminum chloride, or they may be extracted oils produced by solvent extraction with solvents such as phenol, sulfur dioxide, etc. Hydrogenated oils or white oils may be employed as well as synthetic oils resembling petroleum oils, prepared, for example, by the polymerization of olefins or by the reaction of oxides of carbon with hydrogen or by the hydrogenation of coal or its products.

For the best results the base stock chosen should normally be an oil which with the new additive present gives the optimum performance in the service contemplated. However, since one advantage of the additives is that their use also makes feasible the employment of less satisfactory mineral oils, no strict rule can be laid down for the choice of the base stock. The additives are normally sufiiciently soluble in the base stock, but in some cases auxiliary solvent agents may be used. The lubricating oils will usually range from about 35 to 150 seconds (Saybolt) viscosity at 210 F. The viscosity index may range from 0 to 100 or even higher.

Other agents than those which have been mentioned may be present in the oil composition. such .as dyes, pour point depressants, heat thickened fatty oils, sulfurized fatty oils, sludge dispersers, antioxidants, thickeners, viscosity index improvers, oiliness agents, resins, rubber, olefin polymers, and the like.

Assisting agents which are particularly desirable as plasticizers and defoamers are the higher alcohols having preferably 8-20 carbon atoms, e. g., octyl alcohol, lauryl alcohol, stearyl alcohol, and the like.

In addition to being employed in lubricants, the additive of the present invention may also be used in other hydrocarbon oil products such as motor fuels, heating oils, hydraulic fluids, torque converter fluids, cutting oils, flushing oils, turbine oils, transformer oils, industrial oils, process oils, and the like, and generally as antioxidants in mineral oil products.- They may also be used in gear lubricants, greases and other products containing mineral oils as ingredients.

What is claimed is:

1. A composition consisting essentially of a hydrocarbon oil containing 0.02 to 3% of onprous di-(methylcyclohexyl) dithiophosphate.

2. A composition according to claim 1 in which the hydrocarbon oil is a mineral lubricating oil.

JOHN G. MCNAB. NIILO V. I-IAKALA. JOHN P. McDERMOTT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,261,047 Assefi Oct. 28, 1941 2,364,283 Freuler Dec. 5, 1944 2,378,820 Amott June 19, 1945 2,552,570 McNab et al. May 15, 1951 

1. A COMPOSITION CONSISTING ESSENTIALLY OF A HYDROCARBON OIL CONTAINING 0.02 TO 3% OF CUPROUS DI-(METHYLCYCLOHEXYL) DITHIOPHOSPHATE. 